1. Field of the Invention
This invention relates in general to circuits and methods of operating electronic devices, and more particularly, to circuits for driving an electronic component and methods of operating electronic devices including the circuits.
2. Description of the Related Art
Organic electronic devices have attracted considerable attention since the early 1990's. Examples of organic electronic devices include Organic Light-Emitting Diodes (“OLEDs”), which include Polymer Light-Emitting Diodes (“PLEDs”) and Small Molecule Organic Light-Emitting Diodes (“SMOLEDs”). Display devices, including OLED displays, have played an important role in modern human life. As computing, telecommunications, home entertainment, and networking technologies converge, the display unit will become more important.
In the display area, there are many kinds of technologies including cathode ray tube (“CRT”), liquid crystal display (“LCD”), inorganic LED displays, and so on. LCD and inorganic LED displays may include transistors within pixel circuits. Metal-insulator-semiconductor field-effect transistors (“MISFETs”) may be susceptible to changes in threshold voltage due to charges that become trapped within a gate dielectric layer. In the case of LCD and inorganic LED displays, the transistors within driver circuits are on for relatively short amounts of time, and therefore, changes in threshold voltages are not a significant problem in LCD and inorganic LED displays. However, power transistors within driver circuits for OLED technologies can be on for substantially longer times.
FIGS. 1-3 illustrate circuit diagrams of electronic devices 100, 200, and 300, respectively. Each of the electronic devices 100, 200, and 300 includes an electronic component 110, which in one embodiment is an OLED. The electronic component 110 is connected to a field-effect transistor 102, which has a gate dielectric layer that is susceptible to trapping charge. In FIG. 1, the gate electrode of the field-effect transistor 102 is connected to a data holder unit 104, which is connected to a select unit 106. The data holder unit 104 may include a capacitive electronic component having one electrode connected to a first power supply line (e.g., Vdd) and the other electrode connected to the gate electrode of the field-effect transistor 102. The select unit 106 may include a transistor or switch. An optional anti-degradation unit (not shown) may be used and typically is connected to a power supply line and the data holder unit 104.
In FIG. 2, the data holder unit 204 includes a capacitive electronic component having one electrode connected to the gate electrode of the field-effect transistor 102 and the other electrode connected to an anode of the electronic component 110. FIG. 3 is similar to FIG. 2 except that the electronic component 110 is connected to the first power supply line, and the data holder unit 304 is connected to a second power supply line (e.g., Vss).
Unlike MISFETs in LCD or inorganic LED displays, the field-effect transistor 102 in FIGS. 1-3 is on for substantially longer periods of time when the electronic component 110 is an OLED. For example, in an LCD display, a MISFET used within the driver circuit is on for approximately 0.1% of the time, whereas in an organic electronic device, the field-effect transistor 102 can be on substantially all the time. The optional anti-degradation unit addresses degradation of the organic material within the electronic component 110 but does not address the threshold voltage shift seen with field-effect transistors.